1. Field of the Invention
The present invention relates to a vehicle behavior control device equipped with sideslip prevention controlling means that prevents a sideslip by controlling the vehicle and driving-force-distribution controlling means that controls driving-force distribution with respect to at least left and right driving wheels.
2. Description of the Related Art
In recent years, there have been proposed and put in practical use various technologies for vehicle-behavior control, which include braking-force control and driving-force distribution control. Specifically, driving-force distribution control involves controlling the driving force distributed to the front and rear wheels in addition to actively controlling the driving force distributed to the left and right driving wheels, and thus allows for enhanced stability and yawing performance of the vehicle.
For example, Japanese Unexamined Patent Application Publication No. 2006-29460 discloses a technology for controlling the driving-force distribution between the rear left and right wheels. In this technology, feedback control with respect to a difference between left and right wheel speeds is performed first. Specifically, this feedback control includes determining a target wheel-speed difference between the rear left and right wheels on the basis of the steering-wheel angle and the vehicle speed, and setting a first basic control amount for a left-right driving-force distribution mechanism such that the actual wheel-speed difference between the rear left and right wheels matches the target wheel-speed difference. Moreover, yaw-rate feedback control is performed, which includes determining a target yaw rate on the basis of the vehicle speed, the yaw rate, and the steering-wheel angle, and setting a second basic control amount for the left-right driving-force distribution mechanism such that the actual yaw rate matches the target yaw rate. Then, a value obtained by multiplying the first basic control amount by a predetermined gain is added to a value obtained by multiplying the second basic control amount by a predetermined gain, so as to control the driving-force distribution with respect to the rear left and right wheels. In this manner, an oversteer condition and an understeer condition of the vehicle can be suppressed.
Japanese Unexamined Patent Application Publication No. 2006-117113 discloses a technology for appropriately controlling a vehicle in various running conditions by performing front-rear driving-force distribution control and rear-left-right-wheel driving-force distribution control to the maximum effect. First, in this technology, a front-rear-driving-force-distribution coordinative-control additional yaw moment is determined by multiplying a front-rear-driving-force-distribution-control additional yaw moment by a front-rear-driving-force-distribution coordinative-control gain, and a left-right-driving-force-distribution coordinative-control additional yaw moment is determined by multiplying a left-right-driving-force-distribution-control additional yaw moment by a left-right-driving-force-distribution coordinative-control gain. If the vehicle is determined to be on a high μ road in a steering and accelerating state, the front-rear-driving-force-distribution coordinative-control gain is set to a low value so as to reduce the control amount by the front-rear driving-force distribution control. If the vehicle is determined to be on a low μ road, the rear-left-right-wheel driving-force-distribution coordinative-control gain is set to a low value so as to reduce the control amount by the left-right driving-force distribution control. By performing control in this manner, the driving performance can be enhanced at the time when the vehicle is driven on a high μ road in a situation where the lateral acceleration is high. On a low μ road, the above-described control can prevent an excessive yaw moment from being produced when the vehicle is steered by a great amount.
However, problems can occur if the left-right driving-force distribution control as disclosed in Japanese Unexamined Patent Application Publication No. 2006-29460 is performed in combination with vehicle drive control for controlling a vehicle for sideslip prevention, such vehicle drive control including controlling of the engine by opening and closing of the throttle valve and fuel cut and controlling of the braking force independently for the four wheels. In detail, in a case where the driver performs a steering operation, such as turning back the steering wheel continuously during slalom driving along a continuous curve or driving on a low μ road, a yaw moment may undesirably be added by left-right driving-force distribution control in a direction for facilitating an oversteer condition while the oversteer condition is simultaneously being suppressed by vehicle drive control. In that case, the oversteer suppressing performance may deteriorate, or the driving force applied in accordance with the left-right driving-force distribution control may interfere with the braking force, making it difficult to obtain a target braking force and thus deteriorating the oversteer suppressing performance. This phenomenon similarly occurs in Japanese Unexamined Patent Application Publication No. 2006-117113.